“Now what?...” - Part 2

We concluded Part 1 by quoting the frequently promoted view that 2018 could turn out to be the make-or-break year for TB. In turn we start this one by speculating that the same could be the case for Moxafrica.

But first we want to put a few numbers out there simply to provide context – the context being what real chance you have of full recovery if you happen to be infected with either MDR- and XDR-TB this year.

Here’s the first statistic: Only 110,000 MDR- and XDR-TB cases were put on treatment in the last available year of record (2014).

That may sound quite a lot, but the WHO reckons, meanwhile, that there were around 600,000 new MDR cases that same year which means thats only about one-in-six are getting treatment. But this doesn’t get anywhere near telling the whole story. This is mainly because TB is such a slow-burning disease, and because of this there were without any question a host more MDR cases out there in 2014 who weren’t included as new (incident) cases. These would have been the many who had survived untreated from the year before and the year before that (so the bottom line is that there have to have been actually many more potentially infectious cases in 2014 than those 600,000). These unfortunate individuals would be referred to in epidemiology parlance as ‘prevalent’ cases.

For some curious reason the WHO has dumped publishing any prevalence estimates in its TB Reports (we say that this is ‘curious’ not just because the organisation actually relies on prevalence surveys for its best estimates of both incidence and case detection rates both of which are vital to evaluate progress, but also because it’s surely important to have some sort of handle on how many cases might really be out there untreated at any one time given that many of them will be infectious). Given the dearth of existing surveillance of DR-TB and the variabilities of survival times, however, there’s understandably a massive amount of uncertainty as to exactly how many this prevalent number might really add up to.

We’re certainly not averse to taking stabs at such numbers ourselves but in this case we can perhaps more authoratively simply quote from the webinar we reported on in the last blog (part 1), specifically from Francesca when she reckoned on an ongoing prevalent MDR host that’s between 1.2 and 1.8 million (a number which must also surely be slowly growing year on year).

We think that if the WHO and its Health Assembly (and the health ministries of every single WHO member country who signed up to the Plan to End TB) are really serious about ending this pandemic then they should surely start thinking about what this means in 2018.

Here’s what it means as far as we figure it out.

Currently the WHO officially report that only somewhere around one-in-five MDR cases are getting picked up and treated. Here’s a pictorial presentation of this as taken from the most recent Global Report.

The global MDR-TB cases who are actually detected are shown in purple and the number actually enrolled on MDR-TB treatment are in green (and you may well note with concern that this is flatlining exactly when it should be spiking upwards and also the two lines are currently diverging). You can then compare these two lines with the best estimate of the number of incident cases of MDR/RR-TB in 2016 (the blue blob in the middle of a vertical line of uncertainty in the top right of the graph), and you can see that there’s a massive gap between green and blue.

But of course this doesn’t include the prevalent cases. If we were to factor in 1.2 million prevalent cases (the bottom end of Francesca’s estimate) into this graph then this gap would instantly double and become a truly gaping chasm. (And if we were to factor in her 1.8 million it would effectively treble).

And then if we care to consider that only half of those treated (those in the green line) actually see cures at all then these gaps widen further still.

We can make numerical sense of these gaps this way: at best, only one-in-ten new cases sees cure, but actually those numbers must be seen to be disingenuous in the light of prevalent numbers. Using the lower end of Fancesca’s prevalence estimate, it actually means that at best only one-in-eleven prevalent cases with MDR-TB get treatment in any year, with only one-in-twenty successfully treated (with half of these left permanently deaf). So only one in forty get off clean.

When it comes to XDR-TB the situation seems even more dire.

In 2014 (the most recent year for which information is available) a total of 6,077 XDR-TB patients were put on treatment with a global 30% rate of cure (i.e. there were fewer than 2,000 confirmed recoveries).

Despite XDR-TB being identified as a critical public health threat back in 2005, there are sadly still no real estimates for XDR-TB numbers beyond a blanket guesstimate that around 10% of MDR-TB cases are actually XDR. So if we have been having 600,000 new MDR cases each year as the WHO estimate, then the best guess we can make is that around 60,000 of them must be XDR, which means that only one in ten of them (6,077) are diagnosed and put on treatment. And if only one-in-three-and-a-bit are cured it means that the basic cure rate is around one in thirty-three. But again we can anticipate a background prevalence of XDR disease comprising survivors from previous years, and using Francesca’s MDR incidence/prevalence ratio we can suggest that this means there would be 120,000-180,000 XDR cases (out there and potentially infectious with what is essentially lethal incurable disease). So using the lower end of the estimate this suggests that only one-in-sixty-six XDR cases successfully recover from their infection (and half of them will be deaf).

All of this gives us a more proper context for us to answer that disarming question which was posed to the TB experts in the webinar (see Part 1) which was this – if we were to find ourselves diagnosed with MDR-TB what treatment would we want for ourselves?

And we’ll do this in Part 3 in which we’ll also set about answering ‘What’s next for Moxafrica?’ as well..